Nine patients with intraocular tumors were irradiated with protons at the Harvard Cyclotron from July 1975 to date. Those included seven patients with malignant melanomas of the choroid, one with malignant melanoma of the ciliary body and one with choroidal metastatic carcinoid. Each patient received five proton beam treatments (the patient with metastatic carcinoid received four) over eight to ten days totalling 4,000 to 8,000 rads at the tumor. No complications occurred during the treatment or follow-up period, which, at the time of writing ranges from a few days to 21 months. The only adverse effect was minimal epilation (loss of a few eyelases) in two patients and a small erythema of the lid in two patients which eventually disappeared. No further growth has been observed in any patient. Different signs of tumor regression have been observed. Resolution of the serous retinal detachments that accompanied two of the tumors was the earliest finding. Pigment changes over the surface of the tumor and adjacent pigment epithelium was the usual tumor response. Fluorescein angiography showed initially decreased leakage of dye and, later, destruction of the tumor's vasculature and elimination of fluorescein leakage. Only large choroidal vessels remained patent. Ultrasonography revealed decreased height of the tumors post-irradiation and the results of P32 uptake test which was repeated in two patients post-irradiation turned negative. A new on-axis TV viewing system has been used during the treatment of the last patients. This system allowed us to monitor eye movements during all phases of preparation and treatment, to eliminate parallax and use lower levels of illumination with reduced patient's discomfort. Several modifications have been made on the head holder and the ease and safety of patient immobilization has been improved.